Why is euthanizing animais legal, but humans with cancer, uncurable diseases in certain places not?

Morality. Plus humans are obviously much different than animals. Most people would rather live out their short lives than be euthanized. Not to mention most families wouldn't agree to it. So that's why it's not legal. There's probably alot of other legal reasons why but idc enough to research it.

I guess some families are against it because they think it's suicide ! inhumanity
or religion beliefs!

Why do you need permission to be euthanized? Man up and spend like $200 on a single shot shotgun for yourself